Constant current transformer



July 16, 1935. w EsT 2,008,531

CONSTANT CURRENT TRANSFORMER l Filed March 27, 1955 2 Sheets-Sheet 1 8 do 20 29 I,

. r k i 5 /a I I I 1 /6 /4,

I r I l I l I M I I I I Inventor:

Horace 6.Wiest,

F His Attorney.

July 16, 1935. H, w T 2,008,531

CONSTANT CURRENT TRANSFORMER Filed March 27, 1935 2 Sheets-Sheet 2 Inventor: Horace G.Wist,

Att orn ey.

Patented July 16, 1935 UNITED STATES CONSTANT CURRENT TRANSFORMER Horace G. Wiest, West Lynn, Mass, assignor to General Electric Company, a corporation of New York Application March 27, 1935, Serial No. 13,271

6 Claims.

My invention relates to constant current transformers and more particularly to that type of constant current transformer in which one of the windings is pivotally supported at one side and suspended at the other side from a lever mechanism arranged to regulate the position of the movable coil to maintain constant current in the secondary winding. In transformers of this general type it has been customary to use a simple lever pivoted or fulcrumed near its center, one end being connected to the movable winding and the other end carrying a weight to balance the winding. This arrangement, however, cannot maintain an absolutely constant secondary current throughout the full load range of the transformer. An absolutely constant secondary current is in many cases very desirable however, particularly for street lighting circuits where any increase above the normal current will shorten the life of the lamps and unnecessarily increase the consumption of energy, and any decrease below the normal current will result in poor illumination.

Assuming that constant current is maintained, then the magnetic repulsion between the two windings of the transformer is a force which is absolutely constant for all positions of the movable coil and which acts on that coil along the axis of the core leg surrounded by the winding. The center of gravity of the movable winding, however, moves in an arc of a circle about its pivotal support. If the secondary current is to be so regulated as to have exactly the same value for all load conditions and therefore for all positions of the movable coil, then the upward force applied to the movable coil by the lever mechanism should vary from a minimum value with the windings close together through a maximum value when the movable coil is approximately midway between its extreme positions and finally to another minimum value when the windings are farthest apart. Therefore a substantially constant upward force as applied by a simple weighted lever will apply too much force at the extreme positions of the movable coil and too little force at an intermediate position. It is apparent than that the secondary current will be slightly less than normal for very small loads and for very large loads corresponding to the extreme positions of the movable winding, and will be slightly greater than normal when the transformer is about half loaded. The most satisfactory regulation, therefore, requires that the upward force applied by the lever mechanism be somewhat greater for an intermediate position of the movable coil than for the extreme positions.

The general object of the present invention is to provide a constant current transformer of the pivotally supported winding type with an improved regulating mechanism for maintaining constant secondary current throughout the load range of the transformer.

The invention will be better understood from the following description taken in connection with the accompanying drawings in which Fig.

l is a side view of a constant current transformer provided with current regulating mechanism arranged in accordance with the invention; Fig. 2 is an explanatory diagram of the regul5 lating mechanism; Fig. 3 is a perspective view of the regulating mechanism, and Fig. 4 is a side view of the regulating mechanism indicating its two extreme positions.

Like reference characters indicate similar parts in difierent figures of the drawings.

The constant current transformer shown in Figs. 1 and 3 includes a magnetic core l0 having a central winding leg H and two outside legs i2 with a fixed winding i3 and a movable 5 winding I4 surrounding the winding leg II. The movable winding I 4 is clamped in a frame I5 which is secured at one side to a pivotal support l6 carried by brackets IT on the core 10. The other side of the frame 15 is supported by rods i8 connecting it to the outer end of a single arm lever i9 secured or fulcrumed at its other end to a pivotal support 20 on brackets 2i secured to the core in. Stops 22 are provided to limit the downward travel of the lever 59 and prevent the movable winding 14 or its supporting bracket 85 from striking against the fixed winding 33. A double arm lever 23 is fulcrumed on a pivotal support 24 which is oifset from the pivotal support of fulcrum 20 of the lever 19. The lever 23 has an arm 25 at one side of its support 24 carrying a weight 26 at its outer end. The lever 23 has an arm 21 at the other side of its pivotal support 24, the outer end of this arm 21 carrying rollers 28 held in slots 29 in the lever i9. These rollers 28 and slots 29 form a yieldable connection between the lever arm 21 and the lever 69. The rollers 28 are secured to blocks 30 threaded onto screws 3i on the lever 5 arm 21. The effective direction of the lever arm 2'! is from the pivotal support 24 through the axis of the rollers 28 and the angle between this lever arm 2? and the lever arm 25 of the lever 23 may obviously be adjusted by these ad- 55 justing screws 3! for a purpose which will be explained later.

The lever mechanism which has been described, when its parts are properly proportioned, will apply the necessary variable upward force through the rods it to the movable coil l5 to maintain an exactly constant secondary current in the load circuit of the transformer. In a practical application of the invention, it may be assumed that the weights of the levers l9 and 23 are negligible because they may be approximately balanced and the effect of any unbalance in this lever mechanism as compared to the effect of the weight 26 will be negligible. The weight 26 acting through the lever 23 about its fulcrum 24 produces an upward force at the rollers 28 which is substantially constant at all positions of the lever mechanism corresponding to all values of transformer load between no load and full load. Since the pivotal supports or fulcrums 20 and 24 of the two levers i9 and 23 are offset, the rollers 28 will move back and forth in the slots 29 as the movable winding and the lever mechanism assume different positions. Therefore the moment of this upward force of the rollers 28 on the lever is about the fulcrum 20 will vary for different positions of the lever mechanism, this moment having a minimum value at the extreme positions and a maximum value at an intermediate position. Since the length of the lever l9 from its fulcrum 20 to its connection with the supporting rods i8 is fixed, this variable moment will be transmitted as a variable vertically upward force on the rods i8 and the outer side of the movable winding l4. If the lengths of the various lever arms and the locations of their fulcrums are suitably proportioned and related, then the variable vertically upward force applied to the movable winding by the lever mechanism will exactly equal, at all positions of the movable system, the force required to balance the movable winding to maintain exactly constant current in the secondary winding and the secondary circuit of the transformer.

It may be shown by mathematical calcula- -tion and analysis of the lever mechanism which has been described that the vertically upward variable force applied by the lever mechanism to the movable coil may be determined for any position of the coil from the following expression, reference being had to Fig. 2:

cos (0+ a) 1 F 0 cost] arm 25 from its fulcrum 24 to the center of gravity of the weight 26;

c=the length in inches of the lever i9 from its fulcrum 20 to its connection with the rods l8;

=the angle between the horizontal and the lever arm 21;

t=the angle between the effective weight arm 25 and a line through the fulcrum 20 and the axis of the rollers 28;

e=the distance in inches between the fulcrums 20 and 24 of the two levers;

m=the length in inches of the arm 21 of the lever 23; and

a=the angle between the horizontal and a line through the centers of the fulcrum 20 and 24 of the two levers.

In order to apply the invention to a given transformer of the movable winding type, the vertically upward force necessary to apply to the movable winding to secure the desired exact constant value of secondary current may be calculated for a number of different positions of the winding, ;or these values may be obtained by tests of the particular transformer. As already explained, this force will vary for different positions of the movable winding and will have minimum values for the extreme positions of the winding and a maximum value for an intermediate position. By substituting diiferent arbitrary values for the various terms of the expression which has been given for the force applied by the lever mechanism, a set of values may be found for a lever mechanism which will produce a variable force F corresponding exactly for the various positions of the movable winding and the lever mechanism, to the variable force necessary for exact secondary current regulation.

It is not always easy to calculate exactly some of the characteristics of the transformer, particularly the effective weight of the movable winding. In order to compensate for any small inaccuracy due to this cause some adjustment of the mechanism may be found desirable. The value of the weight 26 may of course always be easily adjusted. The effective length of the lever arm 25 supporting the weight 26 may also be easily adjusted. In the construction shown in the drawings the adjusting screws 3| may be used to adjust the angle t indicated in Fig. 2. With these adjustments, compensation for any inaccuracy in calculation may be made and perfect regulation of the secondary current of the transformer may be secured.

The invention has been explained by describing and illustrating a particular embodiment and application thereof but it will be apparent that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. A constant current transformer including a pivotally supported winding, a lever connected to said winding, a second lever, the fulcrums of said levers being offset, a yieldable connection between said levers, and a weight on said second lever.

2. A constant current transformer including a pivotally supported winding, a lever connected to said winding, a second lever fulcrumed between its ends, the fulcrums of said levers being ofiset. a weight on one end of said second lever, and a yieldable connection between the other end of said second lever and the first lever.

3. A constant current transformer including a winding pivotally supported at one side, a lever fulcrumed at one end, a connection between the other end of said lever and the side of said winding opposite its pivotal support, a second lever fulcrumed between its ends, a weight on one end of said second lever, anda yieldable connection between the other end of said second lever and the first lever.

4. A constant current transformer including a pivotally supported winding, a lever connected to said winding, a second lever fulcrumed between its ends, the fulcrums of said levers being offset, a weight on one end of said second lever, and a connection between the other end of said second lever and the first lever, said connection being slidable along one of said levers.

5. A constant current transformer including a pivotally supported winding, a lever connected to said winding to apply a substantially vertical upward force thereto, a second lever yieldingly connected at one end to said first lever, and a weight on the other end of the second lever, the fulcrums of said levers being offset, and said levers and weight being arranged and proportioned to vary said upward force to maintain constant secondary current in said transformer. v

6. The combination in a constant current transformer of a pivotally supported winding, a single arm lever fuicrumed at one end, a connection between the other end of said lever and said winding, a double arm lever iulcrumed between its two arms, the fulcrums of said levers being ofiset, a weight on one arm of said double arm lever, and a connection between the other arm of the double arm lever and the single arm lever,

said combination being arranged and proportioned to satisfy the expression:

where F=the necessary variable vertical upward force in pounds applied by the single arm lever to the movable winding to maintain constant secondary current in the transformer;

W=the weight in pounds of the weight;

r=the length in inches of the weight arm of the double arm lever;

c=the length in inches of the single arm lever;

=the angle between the horizontal and the single arm lever;

t=the angle between the weight arm and a line through the other arm of the double arm lever;

=the angle between the horizontal and the arm of the double arm lever connected to the single arm lever;

e=the distance in inches between the fulcrums of the two levers;

m=the length in inches of the arm of the double arm lever connected to the single arm lever;

a=the angle between the horizontal and a line through the fulcrums of the two levers.

HORACE G. WIEST. 

